Why can't I see External Network contact's profile picture? I have added a few external network contacts that I know have profile picture, but I can't see them.
This is the expected behavior. Only users within the same organization are expected to be able to retrieve photos in Skype for Business Online. For your reference:
I understand it would be nice if we have this feature in Skype for Business Online. Therefore, I suggest you submit feedback via voting the link below: